1. Field of the Invention
The present invention relates to a gas turbine combustor which can reduce the oscillations due to combustion, a gas turbine, and a jet engine which is provided with this combustor.
2. Description of Related Art
For gas turbines which output shaft power by compressing air as a working fluid and heating it in a combustor, and expanding the thus produced high temperature and high pressure gas in a turbine, and for also jet engines used to directly propel aircraft by the kinetic energy produced by the output of a high speed jet in recent years, there has been demand for a reduction in emissions such as nitrogen oxides (NOx) from the environmental viewpoint.
These gas turbines and jet engines have a compressor, a combustor, and a turbine as their principle components, and the compressor and the turbine are directly connected to each other by a main shaft. The combustor is connected to the outlet port of the compressor, and the working fluid which is discharged by the compressor is heated by the combustor to a predetermined turbine entrance temperature. The high temperature and high pressure working fluid provided to the turbine, in the main casing, passes between the static blades and the dynamic blades attached to the main shaft, and expands, which rotates the main shaft and provides output power. In the case of a gas turbine, the shaft power can be obtained by subtracting the power consumed by the compressor from the total output power, and, the shaft power can be used as a driving source if an electric generator or the like is connected to one end of the main shaft.
In order to reduce emissions, such as NOx and the like, from gas turbines and jet engines, a variety of research and development projects concerning combustors are being carried out. For premixing type combustors, it is known that NOx emissions can be effectively reduced when mixture of the fuel gas and the air is homogeneous. In contrast, when the mixture is not homogeneous, because local high temperature portions occur in the high concentration regions of the flame, large quantities of NOx are generated in the high temperature regions and the total emission of the combustor increase. The invention of Japanese Unexamined Patent application, First publication No. Hei 11-141878 is one prior art disclosing a solution to the problem of an inhomogeneous mixture. This prior art discloses a gas turbine combustor provided with a vane provided with a plurality of small holes at the air inflow side of the combustor to distribute the inflowing air and provide a uniformly mixed gas.
This gas turbine combustor is explained as an example of a conventional gas turbine with reference to FIG. 8 and FIG. 9. In FIG. 8 and FIG. 9, reference numeral 1 is a combustor, reference numeral 2 is an inner cylinder, reference numeral 3 is a premixing nozzle, reference numeral 4 is a pilot burner, reference numeral 5 is a main burner, and reference numeral 6 is a top hat. Between the inner cylinder 2 and the top hat 6, air path 7 is formed for the air flow provided by the combustor.
The air flow provided by the combustor flows into the entrance for the air path 7 after being reversed by nearly 180 degrees as shown in the arrow in the drawing, and is reversed by 180 degrees again at the exit, and flows into the combustor 1. Near the exit or inlet of the air corridor 7, the porous plate 8 provided with a plurality of holes 8a are provided. FIG. 8 shows the example for the porous plate set at the exit.
Accordingly, the flow of air which has passed the vane 8 is homogeneous in cross section, and is provided to the tip of the pilot burner which constitutes the premixing nozzle 3, and to the tip of the main burner 5; therefore premixed air, having a homogeneous fuel gas concentration, is produced, and a reduction in NOx formation can be achieved.
However, the above conventional gas turbine combustor, gas turbine, and jet engine have the following problems. While the combustion of premixed air having a uniform concentration has the advantage of reduced NOx emissions, in contrast, a problem is that the combustion oscillations may occur because of the increase of generated heat per unit volume because the combustion occurs in a restricted area in a short period of time.
Such combustion oscillations propagate as pressure waves, and may resonate with parts which can form acoustic systems such as a casing of a combustor or a gas turbine, and because there is the concern that the internal pressure fluctuations of the combustor may become large, normal operation of the gas turbine and the jet engine is difficult under such conditions.
Also, the turbulence of the air flow provided by the compressor is strong and not readily attenuated, therefore, the combustion tends to be unstable. This instability in the combustion may also give rise to pressure waves in the internal pressure fluctuations in the combustor, these pressure waves may propagate, and may resonate with parts which can form an acoustic system such as a casing of a combustor or a gas turbine in some conditions. Accordingly, there is the concern that the internal pressure fluctuations of the combustor may become large, and normal operation of the gas turbine and the jet engine is difficult under such conditions.
Japanese Unexamined Patent application, First publication No. Hei 6-147485 discloses a gas turbine combustor for burning fuel in lean-burn condition wherein an cylinder of combustor is surrounded by a porous wall-cylinder having a cavity between the internal cylinder and the wall cylinder. In this type of gas turbine combustor, however, the porous wall-cylinder is disposed so as not to intervene plate-fins which are the combustion region, therefore decreasing effect of combustion oscillation has not been achieved sufficiently.
The present invention was made in consideration of the above points, and aims to reduce the combustion oscillations while maintaining a low level of NOx emissions from the gas turbine combustor, and also has the objective of providing a jet engine which operates stably.